Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$98.96	5.635%	$104.5364	$104.54	$104.55	$104.50
Purchase #2	$241.90	11.800%	$270.4442	$270.44	$270.45	$270.40
Purchase #3	$200.54	7.475%	$215.5304	$215.53	$215.55	$215.50
Purchase #4	$112.47	7.497%	$120.9019	$120.90	$120.90	$120.90
Purchase #5	$228.92	11.542%	$255.3419	$255.34	$255.35	$255.30
Purchase #6	$53.89	4.363%	$56.2412	$56.24	$56.25	$56.20
Purchase #7	$224.82	3.699%	$233.1361	$233.14	$233.15	$233.10
7 purchase totals =	$1,161.50		$1,256.1321	$1,256.13	$1,256.20	$1,255.90